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Beaming Power To Medical Chips Deep Inside The Body

Published: Tuesday, May 20, 2014
Last Updated: Tuesday, May 20, 2014
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A Stanford electrical engineer has invented a way to wirelessly transfer power deep inside the body.

A wireless system developed by Electrical Engineering Professor Ada Poon  uses the same  power as a cell phone  to safely transmit energy to chips the size of a grain of rice, paving the way for new ‘electroceutical’ devices to treat illness or alleviate pain.    

Wirelessly transfering power deep inside the body could be used to run tiny  electronic medical gadgets such  as pacemakers , nerve stimulators, or  new sensors  and  devices yet to be developed .   

The discoveries reported today in the Proceedings of the National Academy of Sciences (PNAS) culminate years of efforts  by Ada Poon , an assistant professor of electrical engineering, to eliminate  the  bulky batteries and clumsy recharging systems that prevent medical devices  from being more widely used.   

The technology could provide a path toward a new type of medicine that allows physicians to treat diseases with electronics rather than drugs.  

“We need to make these devices as small as possible to more easily implant them deep in the body and create new ways to treat illness and alleviate pain ,” said Poon.   

The  article  describes  how Poon’s team  built  a n electronic  device smaller than a grain of rice  that acts as a pacemaker . It  can be powered or recharged wirelessly by holding a  power  source about the size of a credit card  above t he device, outside of the body .   

New generation of sensors possible   
The central  discovery is an engineering breakthrough that creates a new type of wireless power transfer that can safely penetrate deep inside the body, using roughly the same  power as a cell phone. As Poon writes in her article, an independent laboratory that tests cell phones found that her system fell well below the exposure levels for human safety.   

Her  lab has  tested  this wireless charging  system in a pig and used it to power a tiny pacemaker in a  rabbit . She is currently preparing  the system  for testing  in humans. Should such tests be  approved  and  prove successful,  it would  still take  several years to satisfy  the safety and efficacy  requirements for  using this wireless charging system in  commercial medical devices .   

Poon believes this discovery will spawn a new generation of programmable microimplants – sensors to monitor vital functions deep inside the body; electrostimulators to change neural signals in the brain ; drug delivery systems to apply medicines directly to affected areas.   

Alternatives to drug therapies
William Newsome, director of the Stanford Neurosciences Institute , said Poon’s work created the potential to develop “electroceutical” treatments as alternatives to drug therapies.   Newsome, who was not involved in Poon’s experiments but is familiar with her work, said such treatments could be more effective than drugs for some disorders because electroceutical approaches would  implant  devices to directly  modulate  activity in specific brain circuits . Drugs, by comparison, act globally throughout the brain.   

 “To make electroceuticals practical, devices must be miniaturized, and ways must be found to power them wirelessly, deep in the brain, many centimeters from the surface,” s aid Newsome, the Harman Family Provostial Professor of Neurobiology at Stanford, adding: “The Poon lab has solved a significant piece of the puzzle for safely powering implantable microdevices, paving the way for new innovation in this field.”   

How it works   
The article describes the work of an interdisciplinary  research team  including John Ho and Alexander Yeh, electrical engineering graduate students in  Poon’s lab ;  Yuji Tanabe, a visiting scholar , and Ramin Beygui , M.D., an Associate Professor of Cardiothoracic Surgery at the Stanford University Medical Center.   

The crux of the discovery involves a new way to control  electromagnetic waves  inside the body .   

Electromagnetic waves pervade the universe. We use them every day when we broadcast signals from giant radio towers; cook in microwave ovens; or use an electric toothbrush  that re charges wirelessly in a special cradle next to the bathroom sink.   

Before Poon’s discovery, there was a clear divide between the two main types of electromagnetic waves in everyday use, called far - field and near - field waves.    

Far-field waves, like those broadcast from radio towers, can travel over long distances. But when they encounter biological tissue, they either reflect off the body  harmlessly or get absorbed by the skin as heat. Either way, far - field electromagnetic waves  have been ignored  as  a potential wireless power source  for medical devices.   

Near-field waves can be safely used in wireless power systems. Some current medical devices like hearing implants  use near - field technology. But their limitation is implied by the name: they can only transfer power over short distances ,  which tends to keep such devices close to the skin and limits their usefulness deep inside the body.   

What Poon did was to blend the safety of near - field waves with the reach of far - field waves. She accomplished this by taking advantage of a simple fact –  waves travel differently when they come into contact with different materials such as air, water or bio logical tissue.   

For instance, when you put your ear on a railroad track, you can hear the vibration of the wheels long before the train itself because sound waves travel faster and further through metal than they do through air.   

With this principle in mind, Poon designed a power source that generated a special type of near - field wave. When this special wave moved from air to skin, it  changed its  characteristics  in a way that enabled  it to propagate  –  just like the sound waves through  the train track.   

She called this new method  mid - field wireless transfer.   

In the  PNAS experiment, Poon used her midfield transfer  system to send power directly to  tiny medical implants. But it is possible to build  tiny batteries into microimplants, and then recharge these  batteries wirelessly using the midfield system. T his is not possible  with  today’s  technologies .   

“With this method, we can safely transmit power to tiny implants in organs like the heart or brain, well beyond the range of current near - field systems,” says  Ho , a graduate student in Poon’s lab and co-author on the paper . 

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